在反应式 stream 中对项目进行分组

Question

Say that I have a finite stream of these objects

class Item {
    private int id;
    private List<Tag> tags;
}

Flux<Item> publisher;

Say that these are the items in the stream:

[
    {"id": 1, "tags": [{"value":"A"}]},
    {"id": 2, "tags": [{"value":"B"}]},
    {"id": 2, "tags": [{"value":"C"}]},
]

I want to group them by id and join the corresponding values together.

[
    {"id": 1, "tag": [{"value":"A"}]},
    {"id": 2, "tag": [{"value":"B"}, {"value":"C"}]},
]

How can I do this on the publisher

Answer 1

You can use collectMultimap which allows you to have Map<K, Collection<T>> :

publisher.collectMultimap(Item::getId)
     .subscribe(groupById -> System.out.println(groupById.toString()));

Output:

{1=[{"value":"A"}], 2=[{"value":"B"}, {"value":"C"}]}